Where the sky touches the sea – an improved description of the air-sea gas exchange

Climate change affects our society in various ways. Accurate climate scenarios are essential to aid decisionmakers and society to adapt to the effects.

Adequate parametrisation of the air-sea exchange of carbon dioxide (CO2) and methane (CH4) is important for such climate scenarios. Currently available parametrisations diverge greatly, in particular in coastal areas. Coastal seas differ from open-ocean dynamics and make 10.5% of the global ocean area.

Most of these parametrisations describe the gas exchange as a function of wind speed even though it is driven by the turbulence in the surface layer of the ocean.This project will study the uncertainties in the air-sea gas exchange descriptions in coastal areas and aims to understand the specific processes that control the exchange.

For this, long-term measurements of the gas flux and oceanic turbulence at two coastal sites (Baltic and North Sea) will be performed. Common methods to measure oceanic turbulence are temporally and spatially restricted.

To overcome this restriction, a novel method (5-beam Acoustic Doppler Current Profiler) will be used.The resulting turbulence-based description of the air-sea gas exchange will be implemented in a hybrid model approach within the global Nucleus for European Modelling of the Ocean (NEMO) model.

This model will allow for assessing the impact of the ocean’s carbon uptake based on the commonly used gas exchange parameterisations compared to the proposed turbulence-based description.